1. Field of the Invention
The present invention relates to an electrolytic device for disinfecting water in a water supply system, by means of the generation of active chlorine, comprising an electrolytic cell which is provided with electrodes over which a voltage difference is applied and a generator for supplying the voltage difference for the electrolytic cell, which generator is driven by the water in the water supply system.
The invention further relates to a method for disinfecting water in a water supply system by electrolysis.
2. Description of the Related Art
The use of electrolysis for disinfecting water is known. Usually sodium chloride (NaCl) is electrochemically converted into chlorine and caustic (as a by-product). The salt dissolves in water under forming of Na+- and Cl−-ions. When said solution is guided through an electrolytic cell, while a voltage is applied over the electrodes of said cell, chlorine (Cl2), oxygen and hydrogen ions are formed at the anode and hydrogen and hydroxyl ions are formed at the cathode.
The chlorine formed at the anode may, depending on the pH, also be present as hypochlorous acid (HClO) or as a hypochlorite (ClO−). Dissolved chlorine, hypochlorous acid and hypochlorite are called “free chlorine” or “free active chlorine” or “active chlorine”. When using (common) tap water having a pH of about 7 to 8 and containing a small concentration of NaCl, sodium hypochlorite will be formed. The quantity of free chlorine to be formed will depend on the wanted concentration and the quantity of water to be treated.
Common equipment for disinfecting water consists of an electrolytic cell, a rectifier to convert mains voltage into direct current and a control to adapt the electric current to be supplied to the electrodes to the water flow rate.
Dutch patent application 1012794 describes an electrolytic device for a water supply system comprising an electrolytic cell provided with electrodes over which a voltage is applied, wherein the voltage difference for the electrolytic cell is at least partially supplied by a generator such as a turbine, for instance a DC turbine, driven by the water in the water supply system. The electrolytic cell and the generator of the electrolytic device according to NL 1012794 can be accommodated in one housing.
In the device according to NL 1012794 the electrolytic cell is placed directly in the fluid flow. A possible drawback of this embodiment is that in general too little chloride will be present in drinking water to actually form hypochlorite. According to the description, however, active compounds ensuring disinfection can be formed also in case chlorine is absent. Said compounds particularly are various free oxygen radicals. In practice it has appeared that for the formation of oxygen radicals not all electrode materials are suitable, but that a very special and expensive type of electrode is required to suppress the formation of oxygen. Another drawback occurring when insufficient chloride is present is that the action of the device can only be shown by actually performing tests on water containing bacteria and checking the killing factor.